A material in which an electrically conductive polymer as a p-type semiconductor and an inorganic compound as an n-type semiconductor are complexed on a nano level is expected to act as a solar cell having a hetero pn junction. For that reason, it has been attempted to create the subject solar cell by the methods described in Patent Documents 1 to 3; however, an optimal fine structure or interface structure therefor has not been elucidated yet. Incidentally, according to Non-Patent Document 1, photoelectric data thereof are such a degree as shown in FIG. 27 (FIG. 3 of Non-Patent Document 1). Furthermore, in order to increase a contact area, it may be considered that it is effective to use an agglomerated structure of nanoparticles as one of junction structures; however, since it is difficult to densely fill solid phases each other, a sufficient effect is not obtained, and such a way is only at an ideal stage yet.
In Patent Document 4, generating efficiency is described as follows.
The generating efficiency is calculated according to the following equation:n=e(Va−Vb)/kT(|nIa−|nIb)  (Equation 1)(n represents a diode factor; e represents an elementary electric charge; k represents a Boltzmann constant; T represents an absolute temperature; arbitrary two points (Va: voltage, Ia: current) and (Vb, Ib) of a current-voltage characteristic graph in which a current value is logarithmically expressed.)
Then, when n is equal to 1 the equation 2 is an ideal diode equation, and as an electric behavior of junction is deviated from the ideal sate, the value of n becomes large.”
Furthermore, it is also described that:
“This diode factor n mainly represents a junction density of the pn junction interface, and when the junction density is high, then n is equal to 1, thereby revealing an ideal interface state. When the junction density is low, the rectification properties become deteriorated. In organic semiconductors, n was conventionally a value of from 2 to 3.”
Here, the junction density of the pn junction interface is considered to be an area (adhesive area) of an electrically conductive polymer closely adhered onto the inorganic particle surface by electrolytic polymerization, and it is also described that when the junction density is high, a photocurrent is observed.
The photocurrent is one of factors determining the generating efficiency together with the voltage. In consequence, the adhesive area is an important factor influencing the generating efficiency.